In a server or network equipment, etc., a semiconductor chip (IC chip) and a plurality of communication modules are mounted on a substrate, which is generally called “mother board”. Here, the processing ability of the semiconductor chip (IC chip) has been rapidly improved along with thinning of the semiconductor manufacturing process, and thus speed enhancement of digital signals to be inputted and outputted to and from the semiconductor chip has been progressed year by year along with the improvement of the processing ability of the semiconductor chip. That is, the speed of digital signals exchanged between the semiconductor chip and IC modules has been improved year by year, where the speed of digital signals to be inputted and outputted to and from a semiconductor chip and communication modules of the next generation is expected to be 25 Gbit/sec, and the speed of digital signals to be inputted and outputted to and from a semiconductor chip and communication modules of the second next generation is expected to be 50 Gbit/sec.
However, the transmission loss during electric transmission of high-speed digital signals is large. In other words, signal degradation of high-speed digital signals during transmission is severe. For example, in a case of high-speed digital signals of 25 Gbit/sec, loss of about 0.8 dB/cm is generated on electric wirings that are formed on a general printed board. Even on electric wirings formed on a high-grade printed board for high-speed signals, loss of about 0.4 dB/cm is generated.